LIFE IN PRIMARY PERIOD 215 



to the primitive Merostomata and especially to Limulus. 

 But Scorpions are essentially carnivorous and confine their 

 depredations to other terrestrial Arthropods. It is certain, 

 therefore, that other terrestrial Arthropods existed during the 

 Silurian Epoch, and this is confirmed by the discovery of the 

 wing of a bug, 1 in these same layers. Bugs are Insects 

 already far removed from primitive forms. Though their 

 metamorphoses are still reduced to the appearance of wings, 

 the mouth-parts are highly modified ; the mandibles 

 and maxillae have been elongated into pointed probes and 

 the inferior labium has become a case in which these stylets 

 are enclosed. A very long time must have elapsed for these 

 primitive parts that still retained notable features of their 

 early condition as legs, to be modified to this extent, and 

 during this period Insects with powerful mandibles — Neuroptera 

 and Orthoptera, at least — must have multiplied greatly. 

 We know but few examples of them, and this is due to the 

 fact that very little of the continental formations of the Silurian 

 period has come down to us. 



It is not absolutely impossible that Insects should have 

 existed already in Cambrian times ; nevertheless, their class 

 seems to have made little progress during the Devonian, for 

 we still find only Neuroptera and Hemiptera. It is not until 

 the Carboniferous that we see a real blossoming of this class. 

 A luxuriant vegetation of Club -mosses, Horse-tails, Ferns, 

 Conifers, Cycads, and Cordaites then clothed the land. Some 

 Club-mosses and Horse-tails attained the dignity of trees, 

 possibly equal in size to our most beautiful Conifers. The 

 atmosphere was hot without the heat being excessive ; the 

 temperature was high but uniform, and the sunlight filtered 

 through a humid and misty atmosphere — a phase through 

 which the planet Venus is probably passing at present. These 

 are conditions thoroughly favourable for Insects, which were 

 then represented chiefly by Neuroptera such as the Ephemeridse, 

 Dragon-flies, and Perlidse, or by Orthoptera such as Phasmidae, 

 Cockroaches, Locusts even, or again by Hemiptera 2 related to 

 our large Fulgoridse, Cicadas, and Bugs. The clear differentia- 

 tion of orders with which we recognize to-day had not yet 

 been achieved. Transitional forms, notably between the 



1 Protocimex siluricus. 



2 Dictyocicada, Eugereon, Fulgorina, Mecynostoma, Phtanocoris. 



